Plastic barrel and method of fabrication



A ril 22, 1969 v T. R. GILL 3, 9

PLASTIC B ARREL AND METHOD OF FABRICATION Filed Feb. 7, 1967 v INVENTOR Tue/was l2. GM

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United States Patent 3,439,900 PLASTIC BARREL AND METHOD OF FABRICATION Thomas R. Gill, Cleveland. Ohio, assignor to GS Equipment Company Filed Feb. 7, 1967, Ser. No. 614,439 Int. Cl. B01f 9/00; 133% 31/00; C23b /78 US. Cl. 259-81 12 Claims ABSTRACT OF THE DISCLOSURE A plastic barrel horseshoe shaped in transverse cross section and formed of a one-piece wall structure, a cover, two circular end plates, and reinforcing ribs. Parts are secured by spin welds. The wall structure is perforated and the inside surface has nodules. The barrel is especially constructed to contain parts for immersion in plating solutions. Spin welding is accomplished by rotating a generally conical plastic plug having a circumferential ridge and inserting the plug while spinning into a conical aperture that is formed in one plastic part and which communicates directly with another plastic part to be joined.

This invention relates to new and improved apparatus and techniques for treating or plating articles, and more specifically to improved plating barrel constructions and methods of fabrication.

Typical article treating or plating apparatus include perforated, hollow cylinders which are generally referred to as barrels and which are used to contain the articles to be processed in suitable solutions, such as plating and cleaning baths and the like. These perforated barrels are suspended in the baths and are rotated by belt or gear drives. The rotation of the barrel causes the articles to tumble around the inside of the barrel so that all surfaces of the articles are exposed to the solution. As is more fully described in US. Patent No. 2,562,084, the barrel may include a permanently open slot so that, when the barrel is rotated in one direction, the solution Will flow through the slot into the barrel and discharge through the perforations. Alternatively, as disclosed in US. Patent No. 2,886,505, the barrel may be completely closed in use and the perforations in its sidewalls depended upon for fiow of the solution into and out of the barrel.

Because plating solutions or cleaning baths are often corrosive in nature, improved barrels have been formed of plastic material essentially inert to the solutions used. One such improved barrel is disclosed, and claimed in the copending application of Thomas R. Gill, Ser. No. 573,741, filed Aug. 1, 1966 and entitled Plating Barrels. Conventionally, such barrels have been of hexagonal shape in cross section and formed of separate panels joined by longitudinally extending ribs.

When such barrels as described above are used, the materials placed Within the barrels subject the barrel walls to a substantial load. In addition, when plastic barrels are suspended in the treating baths, they become heated and more pliable. As a result, the barrels often undergo substantial distortion in use. In particular, it has been found that conventional barrels of the hexagonal shape severely distort under load to a shape Where the lower-most three panels forming the bottom half of the barrel become curved in transverse sections so that the barrel is no longer hexagonal. The stresses and resulting strain or distortion of the barrel is uncontrolled and nonuniform, and failure may occur where stresses are concentrated. With present barrels having wall sections that are normally interlocked, cemented or sometimes heat welded together, the problem of unequal stress and distortion is especially serious because of inherent Weakness at the joints.

In accordance with the present invention, a barrel is provided that overcomes the problems of stress and strain above mentioned, as well as other problems, by a novel and improved construction. To this end, a barrel is constructed of a single wall structure and two barrel heads at opposite ends. The wall structure is shaped in cross section, when empty, in the general contour of a horseshoe. This horseshoe shape corresponds essentially to the shape to which a cylindrical or hexagonal barrel tends to distort when loaded. When the weight is added, and in the case of a plastic barrel when the barrel becomes heated and pliable, the stresses from the weight are evenly distributed about the barrel and localized distortion is minimized or eliminated because the barrel is initially in the configuration to which the forces would tend to distort it. Accordingly, a very strong barrel capable of withstanding heavy loads and stresses is provided.

Other advantages are also attained With the present construction. The new shape of the wall structure provides greater area and strength for a given diameter of the barrel, as compared with conventional hexagonal shaped barrels. As a result especially of the greater inherent strength, up to 30 percent more holes can be provided for the circulation of the treating bath as compared with hexagonal barrels of comparable diameter and wall thickness. More holes promote bettter circulation of solution and current, and the treatment of articles is more uniform. In addition, the improved shape provides a smooth, continuous contour to the barrel so that there is no tendency of parts to stick at corners. Also, the single piece wall structure is inexpensive to manufacture, convenient to assemble, and strong.

Plastic barrels of the present construction are advantageously fabricated by using a spin welding technique. As mentioned, plastic plating barrels have been previously constructed with interlocking parts, or cemented or heat Welded joints. This has often necessitated complex shapes, extra parts, and in many cases time consuming assembly procedures. Moreover, cemented or heat welded joints have not been as strong as desired. In particular, polypropylene barrels cannot be readily cemented and joints formed by heating the parts sufficient to melt and adhere the parts together have been weak. By using spin welding techniques, stronger plastic barrels can be fabricated faster and less expensively than before. In the preferred construction of the present invention, this is accomplished by providing apertures or bores through parts of the barrel and providing mating parts such as studs on other parts to be joined. Space is provided in the aperture for a plug to be inserted after the parts are assembled. Advantageously the space is provided by countersinking the aperture after the parts are assembled to enlarge a portion of the aperture and remove a portion of the mating part. A plastic plug is then spun at a relatively high rate and inserted into an open end of the aperture. The plug is somewhat larger than the aperture and the plug wall does not conform in shape to the wall of the hole. This promotes high friction between the spinning plug and the assembled parts, and suflicient heat is generated to weld the two parts and the plug together, forming an essentially integral connection.

Accordingly, it is an object of this invention to provide a barrel of improved shape and construction having the above advantages, and to provide improved methods of fabricating such barrels. Other objects, features and advantages and a more complete understanding of the invention will become apparent from the following detailed description, when considered in conjunction with the accompanyin g drawing, in which:

FIGURE 1 is a side elevational view of a plating barrel constructed in accordance with the present invention;

FIGURE 2 is a cross sectional view taken along the line 22 of FIGURE 1, and looking in the direction of the arrows;

FIGURE 3 is a longitudinal sectional view taken along the line 33 of FIGURE 2 and looking in the direction of the arrows;

FIGURE 4 is an enlarged fragmentary sectional view of two parts of the barrel and a spaced welding plug, illustrating the manner in which parts are connected for welding; and

FIGURE 5 is a fragmentary sectional view similar to FIGURE 4, diagrammatically illustrating the construc. tion of FIGURE 4 after the welding is completed.

Referring now to the drawing, the new and improved plating barrel is generally indicated by reference numeral 10. The barrel is formed of a generally tubular perforated wall structure 12, circular barrel heads 14, 16 which close the ends of the barrel 10, ribs 18a-e extending longitudinally between the barrel heads, and a cover 20. As shown, each of the barrel heads 14, 16 extends radially outward from the wall structure 12 and defines a pulley having a belt groove 22. Axially aligned central openings 24 in the barrel heads 14, 16 accommodate suitable electrodes (not shown) in the usual manner. A circular hub 17 is secured to the outer face of each barrel head 14, 16 in a shallow central recess 19. A central aperture 25 in each hub is aligned with the aperture 24. The hubs are received in guides to stablize the barrel when it is rotated during use.

The wall structure 12 is formed in one piece and is horseshoe shaped in transverse cross section (FIG. 2). More specifically, the wall structure 12 defines a lower cylindrical portion 12a in the orientation shown in FIG- URE 2 which is circular in transverse cross-section from the radial line AB to the radial line BC. The wall structure 12 above the cylindrical portion 12a defines two relatively flat wall portions 12b, 120 which converge from the portion 12a. The distal edges of the wall portions 12b, 12c respectively terminate in grooves 26 in the ribs 18a, 18e. These ribs 18a, 18a are spaced apart to provide a barrel opening. In the preferred embodiment, the right circular portion of the barrel 10 which is bounded by the wall section 12a encompasses a cylindrical segment greater than 180 degrees and constitutes a major portion of the barrel volume. As shown, the relatively straight Wall sections 12b and 12c, as well as the cover 20, lie within or are encircled by an imaginary continuation of the cylindrical wall portion 12a The wall structure 12 is formed with a multiplicity of openings 28 throughout, and the inner barrel surface defined by the wall structure 12 includes a multiplicity of discrete, rounded, nodules or embossments 30. These nodules 30 are disposed in parallel rows which are oblique with respect to the longitudinal axis of the barrel. The nodules interrupt the surface at locations spaced apart in all directions and also provide passageways about the nodules in all directions. As a result, any part that might stick to the inner surface during treatment is quickly dislodged because it is subject to the impact from other parts moving across the surface between the nodules. The openings or perforations 28 are located between and through the nodules 30 and act as circulation holes.

The preferred barrel 10 may be made of a plastic material, such as polypropylene, polymethacrylate, polystyrene, or the like. Such a barrel is of advantageous low weight and is corrosion resistant.

The wall structure 12 and the ribs 18 are directly connected to the barrel heads 14, 16, with the ribs serving to reinforce the wall structure. To this end, the ribs 18b, 0, d extend axially and in contact with the outer surface of the cylindrical wall portion 120, and the ribs 1'8a, e receive the end wall sections 12b, c in grooves 26, as described above. For additional rigidity, the wall portion 12a can be secured to the ribs 18b, c, d at one or more locations. Improved strength is provided by securing the ribs to the barrel heads by spin welding in a manner to be described subsequently.

The uppermost ribs 18a, 18a in the orientation of FIG- URE 2 provide an opening to the barrel. The ribs 18a, 18e each include a notch 32 with a fiat seating surface 34 running the length of the ribs. The seating surfaces 34 receive opposite edges of the cover 20. The cover 20 is clamped in position by a plurality of clamps 36 which are preferably resilient strips coated with a suitable corrosionresistant material. Each clamp 36 is shown having a hooked end 38, a fiat intermediate portion 40 and a bent end 42. A block 44 is connected to the bent end 42. In use, the hooked ends 38 of the clamps are engaged over the rib 18a and the blocks 44 are tightly engaged against the side of the rib 182. In this clamping position, the cover 20 is forced against the flat seating surfaces 34 by a spacer 46 extending outward from the cover 20.

Various plastic parts of the barrel are secured together by spin welding. To join a hub 17 to a barrel head 14, 16 the hub is fixed in a tailstock of a lathe. The barrel head is secured to the chuck of the lathe, rapidly rotated with the chuck and the two parts are forced together, the hub 17 being received in the recess 19 of the barrel head. The resulting friction creates sufiicient heat between the two parts to melt the palstic between the adjoining surfaces, effecting a weld when the relative rotation is stopped.

The manner in which the barrel heads and ribs are secured together is best illustrated in FIGURES 4 and 5 of the drawings. A rib 18 is shown with a central stud 48 extending from one end. It will be understood that the construction at the opposite end is identical. The barrel head 14 is initially constructed with a plurality of apertures or through bores 49 extending through the axial thickness of the barrel head at locations near the periphery where the ribs 18 are to be fixed. The central stud 48 of a rib 18 is inserted in the aperture 49 from an inside surface 14a of the barrel head. The stud fits tightly within the aperture and is initially longer than shown in FIGURE 4. The aperture 49 is then countersunk at the outside surface 14b of the barrel head, forming an enlarged conical aperture portion 50 and removing a portion of the stud 48.

A plastic welding plug 52 of the same or similar material as the parts to be joined is used to complete the joint and weld the parts 14, 18 together. In the preferred construction shown, the welding plug 52 does not conform to the conical aperture portion 50. Rather, it is formed with an outer surface having two surface portions 54, 56 has a greater diameter than the diameter of the conical aperture portion 50 at a corresponding axial location. This provides greater friction for a given force between the plug and aperture wall and concentrates the heat generated at a localized zone. As a result, a faster weld is obtained. The extent to which the plug 52 is larger than the aperture portion 50 is illustrated diagrammatically by the dotted lines 60, 61 in FIGURE 4. A central aperture 62 is provided in the welding plug 52 to receive plastic from the joint when the weld is made.

To weld the two parts 14 and 18 together, the plug 52 is spun about a central axis passing through the central aperture 62, The spinning is initially begun at a location spaced from the parts 14, 18. After the plug is spinning at a relatively high rate, for example about 3000 rpm, it is forced into the conical aperture portion 50. The combination of relative spinning movement and pressure, along with the frictional resistance to the rotation between the parts generates sufficient heat at the juncture of the three parts 14, 18 and 52 to melt the plastic in the area of the juncture and weld the three parts together. The shape of the plug, that is, the ridge or narrow circular zone 58 of larger diameter than the aperture, formed where surfaces 54, 56 meet, assures the rapid welding of the parts. This is because the narrow circular ridge first contacts the receiving aperture 50 and increases the pressure at the location of contact by virtue of the small area. This increases the friction and heat, and concentrates the heat generated in the narrow zone of contact. As plastic melts and the plug 52 is seated in the portion 50 of the aperture, excess plastic from the initially larger diameter portion of the plug flows not only between the parts but also into the central aperture 62 of the plug. This helps assure a complete and uniform joint between the parts. The final weld is depicted diagrammatically in FIGURE 5. Although for purposes of illustration the identity of the separate parts is shown in phantom, it is believed that the plastic fuses at the junctures into essentially a homogeneous mass.

The manner and speed at which the plug 52 is rotated and the pressure with which it is applied in place will vary with different materials and can easily be determined in practice. By way of example, when the parts and plug are of polypropylene, it is sufficient to mount the plug on a drill press spindle as by adhering it to the end of rod in a drill press chuck, and spin it at a speed of about 2500 to 3000 revolutions per minute and then force the plug in place by lowering the spindle with the drill press handle. The resulting connection is extremely strong because the parts have become monolithic. Moreover, the process is rapid and simple. Similar welds can be applied to secure the wall structure 12 to the ribs 18b, c, d if desired, by providing apertures through the ribs, positioning the ribs against the wall, and rotating a plug within each aperture. For such welds it is not necessary that studs from the wall structure extend into the apertures of the ribs.

In use, the barrel is filled by removing the cover 20 and placing the parts to be treated within the wall structure 12. The parts are supported by the wall structure 12 and the ribs 18. Due to the initial shape of the wall structure 12, the additional load from the parts being treated results in little or no change in shape and the stresses from the additional load are relatively uniformly distributed throughout the container. The cover 20 is placed on the seating surfaces 34 and the clamp 36 are secured in position.

In its illustrated form, the barrel 10 is adapted to be incorporated in apparatus such as disclosed in US. Patent No. 2,562,084. As is more fully described in that patent, endless belts are provided which not only rotate the barrel but carry the weight of the barrel and its contents. When embodied in that type of apparatus, the lightweight barrel 10 of this invention provides an important advantage in reducing the stresses imposed upon the belt drive. At the same time, the improved barrel construction is rugged and will support heay loads. The barrel may of course be used with equal advantage in apparatus of the type in which the barrel is suitably journaled and rotated by a gear drive.

In order to treat the articles within the barrel, the barrel is lowered into a bath of treating liquid and is rotated. The large number of openings 28 in the wall structure 12 facilitate circulation of the liquid throughout the barrel. As mentioned above, the higher strength provided by the novel contour of the wall structure 12 permits a larger total hole area in the barrel and thereby assure improved circulation of liquid throughout the barrel. For example, 30 percent more holes can be provided in a plastic barrel constructed in accordance with this invention than in a hexagonal plastic barrel of the same diameter while maintaining adequate strength. The one piece curved construction of the wall structure 12 prevents parts from lodging in corners, as they tend to do in the generally used hexagonal barrels. In addition, the barrel is less expensive to construct than hexagonal barrels with their greater number of parts and more complex interlocking shapes. When the barrel is rotated, the raised nodules 30 prevent articles being treated from sticking to the inside Wall structure 12 and thereby closing the circulation holes 28. The nodules 30 also act to urge the articles toward the center of the barrel in order to promote optimum tumbling action and uniform surface treatment.

During treatment, the plastic material of the barrel 10 becomes more pliable due to the higher temperature of the treatment bath. While in the past this has resulted in undue distortion of hexagonal type barrels, with the present invention such distortion is minimized. Because the barrel is already in the shape to which the forces acting upon it would tend to distort it, there is little or no resulting distortion. As a result, a greater effective strength is achieved.

What is claimed is:

1. An improved barrel of the type for holding articles which are to be processed in a liquid bath and which is adapted to be supported and rotated while immersed in a liquid bath to cause the articles to tumble within the barrel, said barrel comprising end walls, a perforated side wall structure extending between said end Walls which is horseshoe shaped in cross section when the barrel is empty, said wall structure including a curvilinear portion located at one side of an imaginary plane passing lengthwise through the barrel transverse to its end walls and terminal portions which are spaced apart to define an opening extending lengthwise of said barrel on the opposite side of said imaginary plane from said curvilinear portion, said terminal portions being formed on a larger radius of curvature than said curvilinear portion and being convergent from said curvilinear portion toward opposite sides of said opening, and a cover for closing said opening.

2. A barrel as defined in claim 1 wherein the perforated wall structure is formed of one piece.

3. A barrel as defined in claim 1 wherein the side wall structure and end walls are made of plastic.

4. A barrel as defined in claim 3 including reinforcing ribs extending between the end walls outside and in contact with the perforated wall structure, said ribs being integrally connected to the end walls.

5. An improved barrel of the type for holding articles which are to be processed in :a liquid bath and which is adapted to be supported and rotated while immersed in a liquid bath to cause the articles to tumble within the barrel, said barrel comprising a one-piece, perforated wall structure that is horseshoe shaped in cross section when the barrel is empty and has terminal portions defining an opening to the barrel, said horseshoe shaped wall structure having a cylindrical portion forming more than one-half of the barrel and a remaining portion including essentially fiat-walled portions on opposite sides of the barrel opening that converge from the cylindrical portion.

6. In a method of welding plastic parts, the steps comprising:

(a) providing an aperture through a first plastic part,

(b) placing the first plastic part in contact with a second plastic part and with the aperture providing a passageway through the first plastic part directly to the second plastic part,

(c) spinning a third plastic part in the form of a plug that at least partially fits within the aperture,

(d) moving the rotating third plastic part wih force into the aperture,

(e) said speed of rotation of the third plastic part and force with which it is moved into the aperture being sufiicient to cause melting of plastic of the parts, and

(f) thereafter stopping rotation of the third plastic part.

7. The method of claim 6 wherein the third plastic part includes a circumferential ridge and the part is inserted into the passageway and rotated initially with only the ridge contacting the passageway.

8. The method of claim 6 wherein the third plastic part is forced while spinning into contact with the second 7 plastic part as well as into contact with the first plastic part.

9. In a method of joining first and second plastic members, the steps comprising:

(a) forming a hole through said first member,

(b) placing said second member in contact with said first member to close One end of said hole,

(c) placing a plug in the other end of said hole in contact with said first member,

(d) rotating said plug while forcing it toward said second member until said plug and said members have been Welded together.

10. In a method as claimed in claim 9 wherein said second member has a protruding stud portion and is placed in contact with said first member so that said stud portion is engaged in said hole and terminates short of said other end of said hole.

11. In a method as claimed in claim 9 wherein said plug is placed in said hole so that an outer peripheral surface portion of the plug located between its ends is in References Cited UNITED STATES PATENTS 2,836,400 5/1958 Jackson 259-89 2,942,748 6/1960 Anderson 156-73 X 2,956,943 10/ 1960 Hoegh 2042l3 3,058,902 10/1962 Neilson 2042l3 ROBERT W. JENKINS, Primary Examiner.

US. Cl. X.R. 156-73; 204-213 

